Many happy return for Lunt LS50

[Highburymark]

At the end of February I sent my Lunt 50 off to the distributor in Germany to have the old focuser removed. It was stuck tight to the ota, which meant I couldn't use my new Moonlite recently bought from jabeoo - fellow SGL bon oeuf. Good service from Lunt/Bresser, and the scope arrived back yesterday, minus one gnarled and knackered helical focuser, just in time for a sunny weekend's observing. I also thought it would be a good opportunity to clean out the pressure tuner, and replace the O ring and grease on the pressure tuner piston. 

I didn't know quite what to expect when I set the scope up this morning. In particular I was hoping that the internal etalon had survived the journeys to Germany and back, but I've also had issues with the pressure tuner in the past, so I was wondering if the new O ring would make a difference. The session didn't start well. Absolutely no features at all on the sun's disk at all (this was in single stack mode). Tried different eyepieces and played around with the pressure tuner but could make out no discernible detail. 

So I came back indoors, opened up the tuner again, and added a second O ring to the piston. The only problem is the tuner is very difficult to reattach to the brass threading with two rings fitted. Even Lunt itself doesn't recommend two O rings because of the problems reassembling the unit. But there is a solution. If - as normal - you reattach the piston to the black cylinder with the hex end screw - but only tighten the screw 50% (ie leaving the piston to move around a bit inside the black cylinder), I find it is easier to link up the threads and reassemble the unit. 

So back outside, and there was an immediate improvement. Despite the lack of activity on the sun's disk, I was able to enjoy a few small proms and a nice filament. The view wasn't important. It was just a relief to know the scope was in good shape. With the double stack filter however, the scope was once again providing great ha detail.

The new focuser is a joy - beautifully built - though it doesn't provide any extra back focus, possibly slightly less. This means so far I haven't been able to bring my Pentax XF zoom to focus. But happily all my main fixed f/l EPs are fine - TV plossls 15mm and 11mm, Delite 7mm, and most impressively today, the 11mm Nagler T6. What a superb eyepiece the 11mm Nagler is. Delivers stunning planetary and lunar views - as good as any EP I've owned - but I was not expecting it to be as clear and contrastful on the sun. A real bonus.

So I'm happy with the scope, and very happy with the new focuser - looking forward to using it this summer. Though I do wonder if some other owners are putting up with an underperforming scope - when they are just one small O ring away from enjoying the full potential of pressure tuning.

[gnomus]

I've come close to getting one of these a few times, but I keep reading about folks finding the presure tuner somewhat temperamental.  Given my track record with astronomical equipment, I just know I would be one of the ones who had problems.  

I'm pleased you've got yours working well, but if I read you correctly the double stack unit was central to this. 

[Davey-T]

Great result Mark, what grease did you use ? my LS60PT  stopped tuning recently, I think it was because it hadn't been altered for a while and once moved it lost it's seal.

No idea what Lunt recommend but I used red rubber high melting point brake grease as I already had some, worked a treat .

Dave

[Highburymark]

46 minutes ago, gnomus said:

I've come close to getting one of these a few times, but I keep reading about folks finding the presure tuner somewhat temperamental.  Given my track record with astronomical equipment, I just know I would be one of the ones who had problems.  

I'm pleased you've got yours working well, but if I read you correctly the double stack unit was central to this. 

Thanks gnomus. Yes I've had lots of issues with the LS50, but I'd still recommend it to anyone wanting to dip a toe into ha observing. The biggest weakness is the stock focuser - this has been well catalogued on SGL and other sites. The key selling point for the Lunt when launched was its sub-£1k price tag - so they took the decision to use a cheap focuser. Fortunately now there are some excellent alternatives. 

Yes, the double stack filter makes a big difference, though you can get great enjoyment from the scope without it. Most people start off with SS and save up for the DS unit. It's expensive, but far less than double stacking the LS60 (the 60mm double stack filter costs £2k on its own).

What I've experienced is that even if you have problems with the pressure tuner, there are (usually) solutions. Some PTs don't work at all, in which case Lunt or the dealer will replace the scope. Most are fine. I'm somewhere in the middle - and I've managed to make it work well. So I'd definitely recommend the LS50 - it's way ahead of the PST, though if you already own a refractor, the Daystar Quark is worth a look.

[gnomus]

Thanks for the detailed reply.  In fact I have a Quark Chromosphere which I use on my ED80.  I wondered if a purpose-built solar scope might be a better option.  

[Highburymark]

1 hour ago, Davey-T said:

Great result Mark, what grease did you use ? my LS60PT  stopped tuning recently, I think it was because it hadn't been altered for a while and once moved it lost it's seal.

No idea what Lunt recommend but I used red rubber high melting point brake grease as I already had some, worked a treat .

Dave

Thanks Dave,

I think any 100% silicone grease would be OK  - which is what Lunt recommends - Brand I have is McNett, bought from a local hardware store, but sounds as if you've got a good alternative

[Highburymark]

4 minutes ago, gnomus said:

Thanks for the detailed reply.  In fact I have a Quark Chromosphere which I use on my ED80.  I wondered if a purpose-built solar scope might be a better option.  

Ok - I think some quark owners get a LS50 for whole disk views of the sun. Actually the two systems complement each other pretty well. I have an Equinox 80 and have often been tempted by a quark

[Stu]

Very interesting report Mark. Having seen the effect of a sickly pressure tuner it seems a shame that these otherwise beautifully engineered scopes have such problems. Dave's tuner was holding pressure for a very brief time, so I was able to see how good the view can be, but also have the detailed faded out as the pressure dropped.

Fortunately as both you and Dave have found, it seems quite possible to fix by yourself with perhaps a fresh O Ring and some grease.

The 'whole disk vs high power view' discussion will always remain I expect. I generally find myself looking at things at higher power in binoviewers, but still enjoy lower power with cyclops although I don't think I can get full disc. The views are brighter and with more contrast at lower power, but with a shade over your head the contrast holds up very well.

[gnomus]

Yes the Quark has that built in 4.2x barlow (I think that is the figure) and often, just like with my dark sky observing, I find myself yearning for less magnification and 'sharper' views.

[Stu]

1 minute ago, gnomus said:

Yes the Quark has that built in 4.2x barlow (I think that is the figure) and often, just like with my dark sky observing, I find myself yearning for less magnification and 'sharper' views.

Which eyepieces do you use? 32mm and 40mm Plossls seemed best to me to keep the mag down, but 40mm can be a bit like looking through a straw!

[gnomus]

I use a 40mm plossl.